TECTONIC CONNECTIONS BETWEEN SARDINIA AND CALABRIA DURING THE HERCYNIAN AND ALPINE COLLISIONAL EVENTS: CURRENT UNDERSTANDING AND OPEN QUESTIONS

The Sardinia-Corsica and Calabria-Peloritani terranes are fragments of the Hercynian continental-collision belt, extended during Tethyan rifting, involved in Alpine collision, and rifted apart during the opening of the Tyrrhenian Sea. Although they are thought to have been neighbors for most of this time, the tectonic role they played in relation to each other during each of these phases is poorly understood.

In the Sardinia block, a late-Hercynian batholith intrudes both kyanite-eclogite-bearing migmatites and a medium- to low-grade fold-thrust belt, followed by post-orogenic ignimbrite eruption. In Calabria, mid-crustal migmatite is the source of granites intruding a low-grade cover sequence.

During the Mesozoic, it is not clear whether Calabria was an independent microcontinent or remained part of the European margin along with Sardinia. Alpine-age blueschist-grade ophiolitic fragments are present in the northern Calabria subterrane, testifying either to a single, long-lasting, west-dipping subduction zone, or to two subduction zones of opposite polarities. Sardinia is weakly affected by Alpine deformation, although there is extensive arc volcanism along the west side of the island.

Several open questions must be answered before the Sardinia-Calabria relationship is understood:

1) Where were Sardinia and Calabria during the Hercynian orogeny? Do they represent adjacent elements, or widely separated parts of the chain?

2) Were slab detachment or delamination important mechanisms in late-Hercynian evolution?

3) Is there a Hercynian-aged suture in Sardinia? If so, does it continue into Calabria?

4) Was Calabria a microcontinent during the Jurassic? If Calabria remained part of the European margin, then there could only have been a single direction of Alpine subduction during the Cenozoic, closing a single ocean basin. If Calabria became a microcontinent, then two subduction zones are required in order to close two ocean basins.

5) What was the relationship between Sardinia and Calabria during the Alpine phase? Was Calabria-Peloritani one or two microcontinents?

6) Did extension play a large role in the exhumation of HP units?

Calabria and Sardinia have not yet received the attention they deserve as places to study and understand the role of ophiolites and mantle involvement in continental collision.